The sodium cation plays a major role in the control of cell division. An increase in intracellular sodium is necessary to initiate mitosis. In cell populations that exhibit uncontrolled proliferation (i.e. cancer) the intracellular concentration of sodium may be increased up to 350%. In-vivo sodium NMR imaging permits direct assessment of the tissue ionic conditions associated with pathologic processes such as malignant tumors. In-vivo sodium NMR images have been obtained for a variety of benign and malignant tumors of the head and neck. Malignant tumors have demonstrated an increased sodium signal whereas benign tumors have a sodium signal comparable to normal brain tissue. The proposed project seeks to develop in-vivo sodium NMR imaging and spectroscopy into a sensitive and selective imaging modality for the diagnosis and management of malignant brain tumors. There are two primary goals in this research. The first goal is to optimize sodium NMR data collection and image processing techniques for maximum signal sensitivity and quantitative accuracy. This will be accomplished by comparing optimized data collection and processing for three separate 3-D volume pulse sequence imaging techniques on both image quality phantoms and in-vivo canine tumors. Although the primary emphasis will be placed upon pulse sequence techniques, Rf coil comparison and optimization will be examined. The second goal is to develop pulse sequence techniques for differentiating intracellular from extracellular sodium. These techniques involve the use of chemical shift reagents and pulsed field gradients for the determination of molecular diffusion coefficients. The ability to differentiate intra- from extracellular sodium will greatly enhance the clinical selectivity for this NMR modality.